The present invention relates to a progressive ophthalmic lens and in particular to a progressive ophthalmic lens exhibiting improved functionality and ease of adaptation, particularly for the first-time or part-time wearer, and taking into account wearer sensitivity to swim, and to a process for producing such lenses.
Numerous progressive lenses are known in the prior art. Progressive lenses have heretofore been designed on the basis that they have distance, near and intermediate viewing zones. The intermediate zone joins the near and distance zones in a cosmetically acceptable way, in the sense that no discontinuities in the lens should be visible to people observing the lens of the wearer The design of the intermediate zone is based on a line called the xe2x80x9ceye pathxe2x80x9d along which the optical power of the lens increases more or less uniformly.
However, prior art progressive lenses present the wearer with significant adaptation difficulties. For example, a wearer who utilises progressive lenses for reading purposes may generally be inconvenient t)y the limited width of vision for near tasks. Similarly, new progressive spectacle wearers may be sensitive to swim and may be unable or unwilling to learn new head postures dictated by prior art progressive lenses.
It would be a significant advance in the art if the progressive lens could more closely relate to the requirements of the individual wearer and to the natural eye movements of a wearer in performing intermediate and near tasks in particular and thus make adaptation to a progressive prescription easier.
Accordingly, it is an object of the present invention to overcome, or at least alleviate, one or more of the difficulties and deficiencies related to the prior art. These and other objects and features of the present invention will be clear from the following disclosure.
Accordingly, in a first aspect of the present invention, there is provided a progressive ophthalmic lens element including a lens surface having
an upper viewing zone having a surface power corresponding to distance vision,
a lower viewing zone having a greater surface power than the upper viewing zone to achieve a refracting power corresponding to near vision; and
an intermediate zone extending across the lens element having a surface power varying from that of the upper viewing zone to that of the lower viewing zone and including a corridor of relatively low surface astigmatism;
the lens surface including
a relatively high, relatively wide lower viewing zone; and
a relatively wide intermediate zone.
The present invention accordingly provides a progressive ophthalmic lens element exhibiting a balance in zone sizes which provides the wearer with significantly improved near and intermediate vision, thus making spectacles including the progressive ophthalmic lenses more acceptable to the first time or part-time wearer, or a wearer with a near vision priority, and making adaptation thereto a much simpler task.
We may estimate the size of she zone on the lens surface available for clear vision by ray tracing the lens in the as worn configuration for a specific object distance and calculating the area within an Add/4 diopter contour of the RMS power error inside a circle of the 22 m radius centred on the geometric centre (GC).
Preferably, the area of the lower viewing zone when ray traced to a 0.4 m object distance is over 150 mm2.
In a further preferred aspect, the progressive lens design according to this aspect of the present invention may be such that the ratio of the area of clear vision of the upper (or distance) viewing zone to the lower (or near) viewing zone is in the range between approximately 2.50 and 3.00.
This clear vision size ratio is indicative of effective relative zone sizes and illustrates the improved balance of zone sizes between the distance and near viewing zones in the ophthalmic lens elements for wearers with a near vision priority according to the present invention.
By the term xe2x80x9cAddxe2x80x9d as used herein we mean surface addition power of the lens element.
In a further preferred aspect the progressive design lens according to this aspect of the present invention includes a surface design of the peripheral regions of the lens to reduce or minimise the phenomenon of xe2x80x9cswimxe2x80x9d. By the term xe2x80x9cswimxe2x80x9d as used herein, we mean wearer perception of the unnatural movement of objects within the visual field during dynamic visual tasks, which may lead to a sense of unsteadiness, dizziness or nausea.
The applicants have found that the lens surface areas that are critical for reducing the swim sensation are within a pair of generally horizontally disposed opposed segments approximately xc2x122.5xc2x0 above and below a generally horizontal axis passing through the fitting cross.
The opposed segments may have a radius of approximately 15 mm from the fitting cross, preferably approximately 20 mm, more preferably approximately 25 mm.
The minimisation of the swimming sensation may be achieved by reducing optical aberrations contributing to swim. A surface correction(s) may provide a reduction in the sagittal addition power within the opposed segments. The surface(s) may be such that the difference between maximum and minimum sagittal addition power is less than approximately 0.75*Add diopters. This may significantly reduce the phenomenon of swim for a wearer, in use.
This may have the result of increasing blur in the peripheral regions of the lower (or near) viewing zone. However, such blur increase in these regions is an acceptable trade-off in achieving wearer satisfaction with the progressive lenses.
In a still further preferred aspect of the present invention, the progressive lens design may exhibit a small amount of addition power (eg. 0.05 D to 0.4 D), proximate the fitting cross depending on the nominal addition power of the lens element and the base curve.
Applicants have found that the introduction of a small amount of addition power at the fitting cross aids the wearer in adapting to the progressive ophthalmic lens, particularly in respect of intermediate vision. The corridor of the intermediate viewing zone is thus effectively extended a small distance into the upper (or distance) viewing zone, allowing peripheral blur values to be reduced and the zone available for clear vision at intermediate distances to be increased.
It will be understood that the ophthalmic lens element according to the present invention may form one of a series of lens elements.
Accordingly, in a further aspect of the present invention, there is provided a series of progressive ophthalmic lens elements, each lens element including a lens surface having
an upper viewing zone having a surface power to achieve a refracting power corresponding to distance vision;
a lower viewing zone having a greater surface power than the upper viewing zone to achieve a refracting power corresponding to near vision; and
an intermediate zone extending across the lens element having a surface power varying from that of the upper viewing zone to that of the lower viewing zone and including a corridor of relatively low surface astigmatism;
the progressive ophthalmic lens series including
lens elements having a base curve suitable for use in providing a range of distance prescriptions for one or more of emmetropes, hyperopes and myopes, each lens element differing in prescribed addition power and including a progressive design including
a relatively high, relatively wide lower viewing zone and
a relatively wide intermediate zone; the dimensions of the intermediate and lower viewing zones being related to the prescribed addition power of the wearer.
The present invention accordingly relates to a progressive ophthalmic lens series exhibiting improved functionality and ease of adaptation, as it takes into account factors including one or more of the following: wearers"" sensitivity to swim and natural eye movements. The progressive lens element within the series also exhibits a distance/near zone balance more appropriate for a part-time wearer or a wearer with a near vision priority than those provided by general purpose prior art progressive lenses.
As stated above, each progressive ophthalmic lens element in a series according to the present invention exhibits a relatively high lower viewing, or near vision, zone. The relatively high lower viewing zone may reduce the need for the wearer to learn new head postures for reading purposes.
Preferably the lens elements having a base curve suitable for emmetropes have an upper viewing zone and lower viewing zone such that the ratio of the area of clear vision of the upper viewing zone to the lower viewing zone is in the range between approximately 2.50 and 3.00.
In a preferred embodiment of this aspect of the present invention, each lens element in the series may have a progressive lens design exhibiting a small amount of addition power proximate the fitting cross; the addition power component proximate the fitting cross being related to the prescribed addition power and/or depth of focus of the wearer.
Preferably, the addition power proximate the fitting cross of a progressive lens element is in the range from 0.05 to 0.40 D, the fitting cross addition power increasing with the addition power for each of the base curves, and with the increasing base curve for each addition power.
The lens elements may exhibit an increase in corridor length within increasing addition power.
For example, for low to medium addition powers from approximately 1.0 D to 2.50 D, the relatively high, relatively wide lower viewing zone may permit useful reading from a point (the highest reading point) approximately 10 to 12 mm below the fitting cross. Thus the effective corridor length is approximately 10 to 12 mm.
For higher addition powers, eg. from approximately 2.50 D and above, the lower viewing zone may permit useful reading from a point (the highest reading point) approximately 12 mm below the fitting cross. Then the effective corridor length is approximately 12 mm. It will be understood that the slight increase in effective corridor length at higher addition powers permits an increased effective lower or near viewing zone size and/or lower peripheral blur.
By the term xe2x80x9chighest reading pointxe2x80x9d we mean the highest point along the eye path where the wearer can read normal size text at the 40 cm reading distance without perceiving the blur. This is equal to the nominal prescribed add minus the effective depth of focus for near vision which is around 0.50 D for a broad range of addition powers.
In a further preferred embodiment of this aspect of the present invention, the progressive lens design of each lens element in this series includes a surface correction to reduce or minimise the phenomenon of xe2x80x9cswimxe2x80x9d.
The surface modification to reduce swim may be provided within a pair of generally horizontally disposed opposed segments generally centred at the fitting cross of each ophthalmic lens element. The opposed segments may extend approximately xc2x122.5 xc2x0 above and below a generally horizontal axis passing through the fitting cross.
The opposed segments may have a radius of approximately 15 mm from the fitting cross, preferably approximately 20 mm, more preferably approximately 25 mm.
The swim surface correction(s) may be such as to reduce optical aberrations contributing to swim. The swim surface correction(s) may take the form of a reduction in the sagittal addition power variations within the segments defined above.
Preferably, the difference between maximum and minimum sagittal addition power within the opposed segments is less than approximately 0.75*Add (in diopters)
In a preferred embodiment of this aspect of the present invention, the progressive design of each lens element within the series exhibits a substantially constant ratio of the area of clear vision of the upper (or distance) viewing zone to the lower (or near) viewing zone for all addition powers. The clear vision zone size ratio may generally be in the range between approximately 2.50 and 3.00.
The generally constant clear vision zone size ratio may thus provide the wearer with a generally constant area for clear ioveal vision independent of addition power.
In a further preferred embodiment of this aspect of the present invention, the progressive lens design of each lens element within the series exhibits a substantially constant area of clear vision on the lens surface within the lower viewing zone for a specified base curve. Accordingly the design of each progressive lens element within the series provides the wearer with a generally constant, improved area of clear vision for near tasks across a range of addition powers.
Preferably, the lens element series according to claim 21, wherein the lens element series exhibits a slight decrease in the area of the zone clear for distance vision on the lens surface inside a 22 mm radius circle centred on the GC and constrained by the Add/4 diopters RMS power error contour ray traced in the as worn configuration for an infinite object distance with increasing base curve.
By the term xe2x80x9ccorridorxe2x80x9d, we mean an area of the intermediate zone of varying power bounded by nasal and temporal contours of tolerable aberration for foveal vision.
The corridor has a xe2x80x9ccorridor lengthxe2x80x9d (L), which corresponds to the length of the segment of the visual fixation locus which extends from the vertical height of the fitting cross (FC) to the vertical height of the near zone measurement point. For example, in a typical lens element according to the present invention, the power progression begins at the fitting cross (FC) height.
By the term xe2x80x9ceffective corridor lengthxe2x80x9d as used herein we mean the length from the xe2x80x9cfitting crossxe2x80x9d (FC) to the highest reading point (HRP) on the lens surface.
By the term xe2x80x9clens elementxe2x80x9d, we mean all forms of individual refractive optical bodies employed in the ophthalmic arts, including, but not limited to, lenses, lens wafers and semi-finished lens blanks requiring further finishing to a particular patient""s prescription. Also included are formers used in the manufacture of progressive glass lenses and moulds for the casting of progressive lenses in polymeric material such as the material sold under the trade designation CR39.
By the term xe2x80x9castigmatism or surface astigmatismxe2x80x9d, we mean a measure of the degree to which the curvature of the lens varies among intersecting planes which are normal to the surface of the lens at a point on the surface.
In a preferred embodiment of this aspect of the invention each lens element includes a surface correction to improve optical properties proximate the peripheries of the lens element. For example, the distribution of RMS power error may be varied proximate the peripheries of the upper (distance) and/or lower (near) viewing zones.
Preferably the distribution of RMS power error exhibits a relatively low gradient proximate the distance periphery and a relatively high gradient proximate the near periphery.
The relative values of these gradients can be quantified by examining the ratio of the maximum vertical rate of change of the ray traced RMS power error along the 12 mm long vertical lines centred on the fitting cross (FC) and horizontally offset 15 mm from the FC, to the maximum horizontal rate of change of the RMS power error at the level of the near vision measurement point (NMP). In a preferred form, this ratio may be less than approximately 0.60 and may preferably vary from approximately 0.40 to 0.60.
In a preferred aspect of the present invention, the location of the corridor of the ophthalmic lens element may be dictated at least in part by the visual fixation locus;
the visual fixation locus being inset generally horizontally nasally below the fitting cross (FC) of the lens element.
By the term xe2x80x9cvisual fixation locusxe2x80x9d, as used herein, we mean the set of points which are the intersection of the lens surface and the patient""s line of sight as he or she fixates on objects in the median plane. The term does not signify a required, continuous eye movement path. Rather, the visual fixation locus indicates the set of points corresponding to variously positioned objects in the median plane.
As will be explained in detail below, the visual fixation locus takes into account the fact that the wearer may or may not use the accommodative reserve for a particular fixation. As a result, points at different locations in the visual fixation locus are provided having a power sufficient for comfortable use at the appropriate object distances.
The fitting cross (FC) is generally located at (O,yFO). The value Of yFC may vary, for example, from approximately 2 mm to 6 mm above the geometric centre of the lens element.
In a still further aspect of the present invention, there, is provided a method of designing an ophthalmic lens element including a first lens surface having
an upper viewing zone having a surface power corresponding to distance vision,
a lower viewing zone having a greater surface power than the upper viewing zone to achieve a refracting power corresponding to near vision; and
an intermediate zone extending across the lens element having a surface power varying from that of the upper viewing zone to that of the lower viewing zone and including
a corridor of relatively low surface astigmatism; the ophthalmic lens element including
a relatively high, relatively wide lower viewing zone; and
a relatively wide intermediate zone,
which method includes
selecting a merit function relating to at least one optical characteristic of the lens to be minimised with an appropriate distribution of the optimisation weights on the lens surface; and
solving the global minimisation problem using the Finite Element Method; and
fabricating an ophthalmic lens element having a lens surface shaped according to said optimised surface description.
The ophthalmic lens element may be formulated from any suitable material. A polymeric material may be used. The polymeric material may be of any suitable type. The polymeric material may include a thermoplastic or thermoset material. A material of the diallyl glycol carbonate type, for example CR-39 (FPG Industries) may be used.
The polymeric article may be formed from cross-linkable polymeric casting compositions, for example as described in Applicants"" U.S. Pat. No. 4,912,155, U.S. patent application Ser. No. 07/781,392, Australian Patent Applications 50581/93, 50582/93, 81216/87, 74160/91 and European Patent Specification 453159 A2, the entire disclosures of which are incorporated herein by reference.
The polymeric material may include a dye, preferably a photochromic dye, which may, for example, be added to the monomer formulation used to produce the polymeric material.
The ophthalmic lens element according to the present invention may further include standard additional coatings to the front or back surface, including electrochromic coatings.
The front lens surface may include an anti-reflective (AR) coating, for example of the type described in U.S. Pat. No. 5,704,692 to Applicants, the entire disclosure of which is incorporated herein by reference.
The front lens surface may include an abrasion resistant coating, e.g. of the type described in U.S. Pat. No. 4,954,591 to Applicants, the entire disclosure of which is incorporated herein by reference.
The front and back surfaces may further include one or more additions conventionally used in casting compositions such as inhibitors, dyes including thermochromic and photochromic dyes, e.g. as described above, polarising agents, UV stabilisers and materials capable of modifying refractive index.